It is well known, of course, to color thermoplastic polymeric compositions using pigments and soluble dyes. (See, for example, Coloring of Plastics, T. G. Weber, ed., John Wiley & Sons, New York, 1979.) Plastics colored with pigments are usually opaque and may lack brilliance of color afforded by soluble dyes. Use of pigments is also often accompanied by problems in storage, blending, uniformity, etc. Some of the deficiencies encountered in the use of pigments can be overcome by use of soluble dyes which give improved clarity and brilliance, but this approach often results in migration and problems related to solvent extraction of the dye from the thermoplastic resins. Some improvement in solvent extraction and migration properties has been achieved by incorporating poly(oxyalkylene) polymer units into colorants. (See U.S. Pat. No. 4,640,690). These colorants have the disadvantage, however, of having a significant portion of their weight consisting of non-colored polymeric composition. U.S. Pat. No. 4,116,923 teaches the incorporation of reactive colorants into cross linked polyester resins and the use of these colored polyester resins in coloring thermoplastic polymers such as polyolefins. Here again, a major portion of the colored polyester resin used to color the polyolefins is "non colored", and thus results in lower tinctorial strength. Further, it is known that one may improve the nonextractability of colorants and UV absorbers in thermoplastic polyesters by copolymerizing thermally stable colorants into the backbone of the polyester composition. (See U.S. Pat. Nos. 4,617,373; 4,617,374; and 4,707,537. This method suffers from the difficulty in finding non volatile, very reactive colorants which will not be lost by volatilization or decomposition during the stages of ester interchange and polycondensation of the polyester preparation.
It is also known that one may color thermoplastic polymeric materials using color concentrates consisting of physical admixtures of polymers and colorants. However, the use of such physical admixtures to color polymeric materials such as polyesters, e.g., poly(ethylene terephthalate) and blends thereof, presents a number of problems:
1. Colorant migration during drying of the colored polymer pellets. PA1 2. Colorant migration during extrusion and colorant accumulation on dies which can cause film rupture and shut downs for clean up, etc. Such colorant migration and accumulation result in time consuming and difficult clean up when a polymer of another color is subsequently processed in the same equipment. PA1 3. Colorants may not mix well, for example, when using two or more color concentrates to obtain a particular shade. PA1 4. Colorants may diffuse or exude during storage of the colored polymeric material.